We first came across an Alpha heatsink
on Kendon's workshop and later on Akiba PC in 1999 - both Japanese
sites are dedicated to all things cooling and computer. Since that first
encounter Alpha gained increasing popularity with Slot 1/A overclockers and
then sort of faded away after a generally brief flirtation with socket A/370
heatsinks. Then, a few a months ago Alpha came back onto the
performance scene with a full-fledged pentium 4 heatsink. Now we
have the PAL8942 to mull over and things are looking... decidedly Alpha.

Making use
of their signature cold-forged aluminum construction with an embedded copper
plate the PAL8942 is big, black, and chocked full of hexagonal
pins. With an aluminum shroud covering the top 1/3 of the pins an
80mm fan can be attached in either a impingement or exhaust manner for optimal cooling. In fact,
we tested the Alpha PAL8942 with the fan in both an exhaust and
in an impingement (blowing down) orientation and found that there was indeed a slight
performance increase with the fan pulling air up through the fins and expelling it
out the top. Previously, we were under the impression (based on tests with
older Alpha heatsinks) that facing the fan down offered the best performance.
The temperature differences were on the order of a degree or two for the most
part.

We were curious about what goes into the making
of an Alpha, whether or not software like Flotherm is used in the fin
modeling or if the design is purely intuitive, or simply trial and error.
Thermal dynamics is still a relatively complicated science, and with dense
designs like the PAL8942, software modeling solutions can apparently become
quite cumbersome to rely on.

In
addition to developing the most efficient heatsink they can, the Alpha
designers also have to contend with what can physically be made by the
cold forging process. "There are rules as to how dense or sparse a pattern can
be. Too sparse, and the tooling may break after several hundred or thousand heat sinks
are forged, due to the tremendous pressure. Too dense, and we may
not be able to forge it. So, we need to come up with the highest performing pattern that
will work within these manufacturing parameters," said Glenn Summerfield the P.D.
Manager of Alpha Novatech.

In fact, in speaking with Alpha we
learned that the PAL8942 was developed from start to finish in just four weeks.
Prototypes of the massive socket 478 heatsink were made with different types of
pins including; hexagon, octagon, square and dimpled. Obviously, the winning
choice was the hexagon shaped pin of which about 530 stick out of the PAL8942.
The hexagon pin type is also used on the PAL8045 and PAL6035. A few other tricks
went into improving the overall performance of the PAL8942 which we'll get into
in just a moment.

One of the biggest factors in any
heatsinks' performance is undoubtedly the base, and specifically its composition.
If too much material is used the base retains heat or doesn't spread it out the
fins/pins quickly enough. Too little material in the base and the largest
amounts of heat energy is concentrated at the center of the heatsink where air
moves less quickly under most fans.

Pointy edged "teardrop"
fins on the side of the PAL8942 help lower the pressure drop of air as it
moves into the fins.

The opposite side of the
Alpha heatsink has normal octagonal pins which populate the rest of the
heatsink.

In the case
of the PAL8942, the heatsink was first developed with
four different combinations of the aluminum base and copper insert before the
ideal thickness of ~3.5mm was selected for the final design.